1. Field of the Invention
The present invention relates to a receiving device including an impedance control circuit and a semiconductor device including an impedance control circuit.
2. Description of the Related Art
In a case where a digital signal is transmitted through a communication line, a part of a signal energy may reflect on a receiving side at a time when signal level changes. Thereby, a ringing, that is, a distortion of a waveform such as an overshooting and an undershooting may occur. Various technologies are suggested for restricting a ringing. For example, U.S. Pat. No. 6,326,803 (corresponding to JP-A-2001-127805) discloses a termination circuit for a communication line. In a case where a voltage of a signal transits between a low level and a high level in the termination circuit of the communication line, an impedance of a terminator is temporarily reduced during a delay time provided by a delay circuit.
U.S. Pat. No. 6,487,250 (corresponding to JP-A-2000-353945) discloses a signal output system in which an output impedance is continuously changed at a time when a level of an output signal changes. U.S. Pat. No. 6,218,854 (corresponding to JP-A-2000-59444) discloses an integrated circuit device in which an overshooting and an undershooting are attenuated by an attenuation circuit and an output terminal of the attenuation circuit is charged and discharged to a power supply voltage and a ground voltage by a charge/discharge circuit.
However, in an actual communication network, a waveform changes on a receiving side in various ways. Thus, even if an impedance is changed for a predetermined time as described in U.S. Pat. No. 6,326,803 or an output impedance is changed on a transmitting side as described in U.S. Pat. No. 6,487,250, a ringing on the receiving side may not be restricted sufficiently. When an overshooting or an undershooting occurs in the integrated circuit device disclosed in U.S. Pat. No. 6,218,854, the attenuation circuit and the charge/discharge circuit uniformly handle the overshooting or the undershooting. Thus, the ringing on the receiving side may not be restricted sufficiently.
JP-A-2007-318734 and JP-A-2006-67543 respectively disclose a semiconductor device coupled with a differential communication line.
FIG. 32 is a schematic diagram illustrating a differential communication network disclosed in JP-A-2007-318734. The differential communication network is provided in a vehicle. The differential communication network includes a plurality of nodes 210 and a differential communication line 212 for coupling the nodes 210 with each other.
Each of the nodes 210 is a sensor for detecting a state of the vehicle or an electronic control unit (ECU) for controlling an actuator based on information from a sensor. The differential communication line 212 is provided for transmitting control communication signals between the nodes 210. The differential communication line 212 is formed of a pair of twisted phase conductors. A differential signal is transmitted through the pair of phase conductors. An electric current that flows in one of the pair of phase conductors has a phase opposite to an electric current that flows in the other one of the pair of phase conductors. Thus, the differential signal creates a potential difference.
Each of the nodes 210 includes a communication circuit. Each of the nodes 210 converts transmitting data and receiving data at the communication circuit in accordance with a communication protocol of the differential communication line and communicates with each other through the differential communication line 212.
The differential communication line 212 extends in a body 214 of the vehicle from front to rear and from left to right. On the differential communication line 212, a plurality of hubs 216 and a through connector 218 are disposed. Each of the hubs 216 includes two bus bars for dividing the differential communication line 212. The through connector 218 is provided so that the node 210 can be freely connected and disconnected with the differential communication line 212 through the through connector 218.
On the differential communication line 212, there is a portion where a plurality of harnesses 220 is arranged in parallel. The harnesses 220 include a communication line used for an in-vehicle system and a power supply line for driving an actuator. In the harnesses 220, a differential harness and a single-end harness that uses the body 214 as a return channel are mixed. A portion where the differential communication line 212 and the harnesses 220 are arranged in parallel is bundled, for example, with a tape and becomes a harness bundle 222. The harness bundle 222 is located at a lower portion of a door that couples a front portion and a rear portion of the vehicle.
In the differential communication network, if a surge such as electro static discharge (ESD) is applied to the pair of phase conductors, a semiconductor device in the nodes 210 may be damaged. In addition, if an overshooting occurs in the semiconductor device at a rising edge or a falling edge of an input signal from the pair of phase conductors, the semiconductor device may malfunction.